1) Field of the Invention
The present invention generally relates to a shock absorber control system which alters the setting (characteristic) of the damping force of each shock absorber provided in a vehicle on the basis of the condition of a road surface on which the vehicle is traveling.
2) Description of the Prior Art
There is previously known a shock absorber control system which switches the setting of the damping force of a shock absorber between a high level (hard state) and a low level (soft state) on the basis of the condition (roughness) of a road surface on which the vehicle is traveling.
Japanese Laid-Open Patent Application No. 64-67407 discloses an arrangement in which it is determined whether or not the road surface on which the vehicle is traveling is rough on the basis of a damping force change rate obtained from an output signal of a piezoelectric load sensor provided in a shock absorber. More specifically, the damping force change rate is compared with a threshold value based on the vehicle driving condition. When the damping force change rate exceeds the threshold value, the setting of the damping force of the shock absorber is altered to the low level (soft state) from the high level (hard state).
In actuality, a sensor for detecting the damping force change rate is provided for a shock absorber provided for each wheel of the vehicle, and a damping force setting alteration control is carried out separately for each shock absorber on the basis of the damping force change rate output by the corresponding sensor. If the sensitivity levels of the sensors provided for the respective shock absorbers are different from each other, the damping force change rates output by these sensors will be different from each other for the same road surface condition. For example, the damping force change rate obtained when the left front wheel runs on a projection on the road surface is different from that obtained when the left rear wheel runs on the same projection. As a result, there is a possibility that the setting of only some of the four shock absorbers are altered under the same condition. In this case, the alteration conditions for the shock absorbers are different from each other, and riding comfort as well as vehicle drivability and stability deteriorate.
In order to eliminate the above-mentioned problem, it is necessary to use sensors which have the same sensing characteristics. However, in actuality, it is very difficult to use sensors which have the same sensing characteristics. It may be possible to initially adjust the sensing characteristics of the sensors. However, the sensing characteristics of the sensors will deteriorate with age even if the initial adjustment is carried out.